Abstract

The aim of this study was to determine the influence of the engraftment site on the tumor biology and drug sensitivity of a panel of hematological patient derived xenografts (PDX). PDX cells (3x10e6 cells/mouse) were injected intratibialy (i.t.), intrasplenal (i.s.) or subcutaneously (s.c.) into NOG (NOD/Shi-scid/IL-2Rγnull) mice. Tumor engraftment was determined by flow cytometry (FC) in bone marrow (BM), peripheral blood (PB) and spleen during the course of engraftment and at the end of a study. Overall survival (OS) served as an additional read-out. In 3 models sensitivity towards cytarabine (Cy) was evaluated. Our group has established 18 PDX of acute leukemia (16 AML, 1 ALL, 1 APL). 16/17 lines engrafted when injected i.t., 10/12 developed tumors after i.s. implantation and 13/14 established tumors post s.c. cell injection. Thus, the overall engraftment capacity was for most of the models not depending on the injection site. Nevertheless, some models could only be propagated in a specific setting: LEXFAM 2713, grew exclusively i.t. or i.s., whereas LEXFAM 2824 could be propagated solely when injected s.c.. The implantation site did influence tumor growth rate: Mean OS ranged from 151.4 (±25.21) days for i.t. to 89.2 (±16.82) days for s.c. propagation. I.s. transplanted mice had to be sacrificed after 91.9 (±17.33) days. The dissemination pattern of individual lines was affected by the injection site. In general, infiltration of the hematopoietic organs was higher when cells were engrafted i.t. or i.s.. Nevertheless, also s.c. implanted, AML cells infiltrated murine PB, spleen and BM, although not consistently and to a much lower extent. Interestingly, the expression pattern of the 6 investigated surface markers (CD45, CD3, CD34, CD33, CD38 & HLA-ABC) was not influences by the application route. Every model depicted its distinct expression pattern irrespective of the application route. Cy was highly active in 1 AML (LEXFAM 2531) and 1 ALL (LEXFAL 2665) model. OS was significantly prolonged in the s.c. as well as in the disseminated setting (p< 0.003, Log-rank (Mantel-Cox) test). Another AML line (LEXFAM 2734) depicted a less pronounced sensitivity towards Cy (p< 0.007, Log-rank (Mantel-Cox) test) both growing s.c. or i.t.. Thus, drug sensitivity was not influenced by the injection site of the leukemic cells. Of note, the PDX drug responses mimicked the responsiveness of the respective donor patient. Taken together the leukemia PDX panel represents the molecular diversity of the disease and mirrors sensitivity towards standard of care. Our recent careful investigation of the subcutaneous approach in these models highlights their suitability for this type of studies. This enhances the value of the platform as it combines the possibilities of a mid-throughput screening enabled by the subcutaneous approach with the general advantages of a patient-derived leukemia model.